CO2 exists in three states, namely gas, liquid and solid. Gaseous CO2 has a specific gravity of 1.53 which makes it heavier than air. Compressing and cooling CO2 gas produces liquid CO2 125. Depressurizing and warming liquid CO2 125 will rapidly transform the liquid to a solid form. Solid CO2 is commonly referred to as dry ice. Dry ice sublimates back to the natural gaseous state. In that regard, sublimation energy can be harnessed for mechanical work.
Liquid Carbon Dioxide (CO2) has long been utilized in the oil industry for well development and rehabilitation. The chemical and physical reactions that occur when liquid CO2 125 interacts with fluids within the confines of a well include, for example, dissolving oil residue by the formation of carbonic acid, removing deposits through mechanical sublimation and pressurization due to sublimation, forcing CO2 through fractures within the oil bearing formation to open pathways for increased oil production.
Groundwater wells (wells) are drilled and lined with casing materials. Casing of well 105 is typically perforated or screened at or below the groundwater level and extends to bottom of the casing to allow water to enter and accumulate. The entire perforated or screened section of the water casing of well 105 and the annulus immediately outside the casing of well 105 is often treated with liquid CO2 125. However, treating the entire screened section simultaneously is not efficient, safe or entirely effective. Rock or sediments penetrated during drilling are rarely homogenous. Water yield is higher through fractured rock or large grained sands and gravels. However, less permeable zones still are important to water production wells. When the entire screened interval of a well is treated with liquid CO2 125, it will preferentially move out of the screen through the more permeable strata, leaving the less permeable zones outside of the perforated or screened casing 115 untreated. Increasing CO2 pressure would help treat less permeable zones outside of the casing of well 105, but over pressurizing a casing of unknown age or condition would create a safety issue. In addition, while attempting to treat lower permeable zones with increased pressure, large volumes of CO2 would escape through the more permeable zones lowering the efficiency.